"union" like struct in C#

program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using System.Runtime.InteropServices;

namespace ConsoleApp1
{
    [StructLayout(LayoutKind.Explicit)]
    public struct IP_ADDR
    {
        [FieldOffset(3)]
        public byte b1;
        [FieldOffset(2)]
        public byte b2;
        [FieldOffset(1)]
        public byte b3;
        [FieldOffset(0)]
        public byte b4;

        [FieldOffset(0)]
        public UInt32 addr;
    }

    class Program
    {
        static void Main(string[] args)
        {
            IP_ADDR localhost = new IP_ADDR();
            localhost.b1 = 127;
            localhost.b2 = 0;
            localhost.b3 = 0;
            localhost.b4 = 1;

            Console.WriteLine(localhost);
            Console.WriteLine(localhost.addr);
            Console.WriteLine( Convert.ToString(localhost.addr, 2) );
            Console.WriteLine("{0}.{1}.{2}.{3}", 
                localhost.b1, localhost.b2, localhost.b3, localhost.b4);
            Console.WriteLine("{0}.{1}.{2}.{3}",
                Convert.ToString(localhost.b1, 2),
                Convert.ToString(localhost.b2, 2),
                Convert.ToString(localhost.b3, 2),
                Convert.ToString(localhost.b4, 2)
            );
        }
    }
}